Pivot table with condition it subtotal

[Ethel]

Hello, could you please help me with adding special subtotal in the pivot table

my pivot table looks like this: In usual situation Category 1 will be sum of subcat1 and subcat2. But I need  to replace Category 1 numbers with numbers from Category 2. Please see 2nd table. I hope it's possible. Thanks a lot in advance!!!

	Nov				Dec
	Group1		Group2		Group3		Group4
	Subgroup1	Subgroup2	Subgroup3	Subgroup4	Subgroup5	Subgroup6	Subgroup7	Subgroup8
Category1	1	2	3	4	5	6	7	8
SubCat1	0.5	1.5	2	2	2	3	3	2
SubCat2	0.5	0.5	1	2	3	3	4	6
Category2	9	10	11	12	13	14	15	16
SubCat2	9	10	11	12	13	14	15	16

	Nov				Dec
	Group1		Group2		Group3		Group4
	Subgroup1	Subgroup2	Subgroup3	Subgroup4	Subgroup5	Subgroup6	Subgroup7	Subgroup8
Category1	9	10	11	12	13	14	15	16
SubCat1	0.5	1.5	2	2	2	3	3	2
SubCat2	0.5	0.5	1	2	3	3	4	6
Category2	9	10	11	12	13	14	15	16
SubCat2	9	10	11	12	13	14	15	16